Pneumatic tires for severe service applications on heavy vehicles that operate at slow speeds, such as refuse trucks, construction trucks, buses and tankers, are prone to significant heat buildup in the tire crown area. The heat buildup reduces both belt edge durability and crown durability. Conventional pneumatic tires incorporate a belt package that includes multiple cut belt layers wrapped about the circumference of the tire. Typically, the cut belt layers in conventional pneumatic tires for use on such heavy vehicles are formed from a single type of belt wire and are narrower in width than the tire footprint. Conventionally, the width of the widest cut belt layer is less than 90% of the tire footprint. The belt layers are most typically stacked in layers with the cords being oriented equally, but oppositely directed between adjacent layers.
One specific type of pneumatic tire, the 11R24.5 G286 LR ‘H’ tire, for use in severe service applications is constructed with four individual cut belts each formed from a single type of belt wire. Two of the cut belt layers are deemed the working belt layers. The green widths of the working belt layers of the LR ‘H’ tire, which has a footprint width of 7.89″, are 7.00″ and 7.80″, respectively, and the corresponding cured belt widths are 6.40″ and 7.00″, respectively. The cured belt widths are approximately 81% and 89% of the tire footprint, respectively. The contribution of the two working belts alone to the overall tire weight is 14.31 lbs. Individually, the weight contribution for one working belt is about 6.79 pounds and the weight contribution for the other working belt, which is the wider of the two working belts, is about 7.52 pounds.
To solve this durability issue, the inventor John Kotanides Jr. in U.S. Pat. No. 7,267,149 proposed a pneumatic tire for service on heavy vehicles having a belt package with widened belts. The tire included a belt reinforcing structure or belt package having multiple cut belts of which one of the cut belts has a width approximately equal to the tire footprint. Widening two of the cut belts and forming at least one of the widened cut belts from a lighter material serves to improve tire durability in the regions of the tire crown and shoulder without increasing the overall tire weight.
In service applications like commercial bus tires, not only is the crown region subject to high temperatures, but also the bead area adjacent the hot brakes become overheated during use.
Tires under exposure to heavy loads and constant stops for braking such as buses and waste haulers see extremely high service temperatures. These high temperatures reduce the life of the tires. One way to reduce tire heat buildup is to cut the weight of some of the belt layers as the width was increased as was accomplished in U.S. Pat. No. 7,267,149. This is only feasible if the tire is made sufficiently strong for its required service application. A cool running, but inferior strength tire casing is not a workable solution. It is this dilemma that is most difficult and challenging to solve when designing tires for these heavy loaded commercial vehicles such as waste haulers and buses.
For these and other reasons, it would be desirable to modify pneumatic tires for severe service applications on heavy vehicles so as to improve tire durability and stiffness without significantly increasing tire weight.